In JP-A S61(1986)-267580 (EP-A 193256), JP-A H5(1993)-086057 (WO-A 9218501) and Chem. Pharm. Bull., 39, 1440(1991), there are descriptions that thiazolidinedione derivatives having various 2-(2-pyridyl) ethoxy groups show hypoglycemic and hypolipidemic activity and they are useful as medicines.
Methods of producing such thiazolidinedione derivatives as above, those described in, for example, (1) JP-A S63(1988)-139182 (EP-A 257781), (2) Chem. Pharm. Bull., 39, 1440(1991) or (3) JP-A H5(1993)-112483 (EP-A 506273) are known.
In the above-mentioned (1), as a method of producing a benzaldehyde compound, the starting compound of the above-described thiazolidinedione derivatives, there is described a method which comprises allowing 2-(2-pyridyl)ethyl alkane (or allene) sulfonate compound to react with p-hydroxybenzaldehyde in a solvent as exemplified by aliphatic halogenated hydrocarbons, aromatic hydrocarbons, ethers, water, ethyl acetate and dimethylformamide, or in a suitable mixture of them in the presence of a base. When the reaction is conducted in a non-aqueous organic solvent, among these solvents, it takes a relatively long period of time for completing the reaction. Due to .beta.-elimination reaction as the side reaction, 2-vinyl pyridine is produced prevalently to lower the yield and purity of the object benzaldehyde compound, exerting undesirable influence on the yield and quality of the products in the subsequent reaction steps. On the other hand, in the case of conducting the reaction in the two-layer system of the above organic solvent and water, it is necessary to allow a phase-transfer catalyst to exist in the reaction system. Since the solvent employed is not homogeneous, control of stirring conditions is difficult to make the yield and purity of the object benzaldehyde compound relatively low, thus the method disclosed in (1) above is hardly considered industrially advantageous one.
Likewise, in the method described in the above (2), since the reaction is conducted in the two-layer system of methylene chloride and water, use of benzyl tributyl ammonium chloride is required as a phase-transfer catalyst. Since the solvent employed is not homogeneous, control of stirring conditions is difficult, and the method can hardly considered industrially advantageous one.
In the method described in the above (3), since an alkali metal salt or alkaline earth metal salt of p-hydroxybenzaldehyde is employed as a starting compound, a step for isolating such a starting compound in advance is required.
Therefore, it has been desired to provide a more convenient method of producing benzaldehyde compounds useful as starting compounds for synthesizing thiazolidinedione derivatives showing hypoglycemic and hypolipidemic activity in a higher yield and quality.